Ozone generators are used for sterilization and odor killing in refrigerators and rooms, and ozone is used as an oxidant and a sterilizer in plants where chemical and medicinal plants as well as in semiconductor devices are manufactured. This is in addition to conventional use in excrement processing facilities or sewage facilities.
Furthermore, in the production of semiconductor devices, SiO.sub.2 film is used as an interlayer insulation film for A1 wirings, and a CVD (chemical vapor deposition) using TEOS (organic silane) and gaseous ozone of excellent step coverage has been examined for embedding to flatten the grove shape between the wirings.
For general ozone generators, a method of generating a great amount of ozone by silent electric discharge process using air or oxygen as a starting material has been used.
In the silent discharge type ozone generator, a dielectric material is inserted and disposed between electrodes opposed to each other, a high voltage is applied between the electrodes and an oxygen-containing gas is passed through a discharge gap to obtain ozone.
A tubular ozone generator as shown in FIG. 1 has a construction in which a glass tube dielectric material (2) is disposed so as to surround a cylindrical tubular high voltage electrode (1) and a tubular water cooling grounding electrode (4) made of stainless steel is disposed by way of a required discharge gap (3), in which air or oxygen is passed through the discharge gap (3) to obtain ozone, the grounding electrode being a double tube through which a coolant such as water is passed.
In addition, Japanese Patent Publication Sho 51-6110, Japanese Patent Publication Sho 46-42748, etc., propose, cylindrical ozone generators of the similar construction.
Further, a plane type ozone generator as shown in FIG. 2 has a structure in which a pair of high voltage electrodes (10) and a grounding electrode (11), each laminated with a dielectric material (12) on a flat electrode surface, are opposed to each other by way of an insulating separator (13) and air or oxygen is introduced from one of holes in the direction of an orthogonal line in the thus formed electric discharge gap (14) and ozone is obtained from the other of the holes.
In addition, Japanese Patent Publication Sho 45-22930, Japanese Patent Publication Sho 51-6111, Japanese Patent Laid Open Sho. 51-148290, Japanese Utility Model Laid Open Sho 61-125485, etc., propose plate-type ozone generators.
The ozone generators having the respective constructions as described above involve a problem that since dielectric material is impinged by electrons at high voltage upon discharge in a cell in the device, ingredients of the dielectric material such as enamel or glass may intrude into gaseous ozone, or melting of ions or molecules of the electrode may occur to contaminate the generated gaseous ozone.
In view of the above, ceramics with less abrasion, free from leaching of ions or molecules and having high specific dielectric constant have been used for the dielectric material (Japanese Patent Laid Open Sho 55-37483).
Such ceramics are shaped and sintered into various shapes depending on the constructions of the ozone generators, but it can not be said that the moldability is satisfactory and there is a requirement of securing close bondability with the electrode to prevent oxidative corrosion with respect to the electrode (Japanese Patent Publication Sho. 62-7121).
In particular, such an extremely high cleanness as not containing particles, metal ions, etc., is required for gaseous ozone at high concentration used for the semiconductor steps. However, since the ingredients of the matrix of the dielectric material may possibly be incorporated, even though in small amounts, into the gaseous ozone, there is a problem that the utilization in a semiconductor production device is hindered. In view of the foregoing present situation for the ozone generator, it is an object of the present invention to provide an ozone generator capable of disposing a protection film of excellent abrasion resistance extremely easily to the surface of the dielectric material and preventing abrasion of the dielectric material and melting of ions and molecules due to dielectric discharge as an industrially preferable productivity and it is an object thereof to provide a dielectric material having a protection film used for an ozone generator and a method of forming such a protection film.